A new ts donor virus that had been shown to be more stable in vivo and in vitro than the ts-1[E] and ts-1A2 donor viruses nonetheless lost its ts phenotype after in vitro stress at restrictive temperature. Its ts phenotype was also lost during replication in vivo in cyclophosphamide treated hamsters. For these reasons work with ts mutants has been terminated. A reassortant virus containing the hemagglutinin and neuraminidase genes of a virulent human virus and the six internal genes of an attenuated avian virus was produced. This reassortant was attenuated and immunogenic in the hamster. This avian-human reassortant virus lost its enterotropism for ducks but retained its bursal tropism. Additional avian-human reassortants were produced for use in the characterization of the genetic determinants of virulence of influence A viruses for primates and for ducks. Synthetic peptides of the A/Victoria/75 (H3) hemagglutinin were administered to hamsters. The hamsters did not develop an HI antibody response and manifested only minimal resistance to wild type challenge.